This invention relates to an actuator. More specifically it concerns an actuator comprising an actuator housing including a fitting for connecting the actuator to an object, and a motor which via transmission elements drives an output actuator shaft of the actuator, wherein the actuator shaft is rotationally disconnectable from the motor. The actuator shaft is rotatable between two angular positions whereof one angular position may correspond to the object being in a first condition and the other angular position may correspond to the object being in a second condition. The actuator is provided with an element, typically a spring, for mechanically storage of energy, the element, by energy cut-off to the actuator, being releasably arranged to be able to displace a nut being prevented from rotation around its longitudinal axis along a screw thread complementary fitting to the nut and connected to the actuator shaft, whereby the actuator shaft is rotated between the two angular positions.
The following is based on the actuator being utilised for operating a valve. This entails no limitation in the scope of the invention, but serves as a useful basis for explaining the features of the invention.
Electric actuators have among other things, due to their simple connection, seen a considerably increased use. Electrical actuators have, however, according to prior art, a weakness in that they have difficulties in closing a valve in case the electric supply to the actuator fails.
Some actuators are provided with auxiliary equipment for manually rotating or displacing the actuator output shaft to a position wherein the valve is closed. Such auxiliary equipment is of no avail if the actuator is situated in a position where access is difficult, such as submerged.